Marine drive unit with gyrostabiliser

ABSTRACT

The invention provides a marine drive unit ( 1 ), such as an outboard motor, for a marine vessel, comprising: an engine or power plant (E), such as an internal combustion; a drive transmission for transmitting or transferring mechanical power generated by the engine or power plant (E) to a propeller shaft for generating propulsion for the vessel; a casing ( 3 ) that houses or at least partially encloses the engine (E) and/or the drive transmission; a mounting assembly ( 2 ) configured to mount the marine drive unit ( 1 ) to a hull, preferably to a transom, of the marine vessel; and a gyrostabiliser ( 4 ) arranged in or on the mounting assembly ( 2 ) or the casing ( 3 ). As an alternative to an outboard motor, the marine drive unit ( 1 ) may be provided as a stern drive unit or a pod drive unit. The invention also provides a marine vessel incorporating such a drive unit ( 1 ).

FIELD OF THE INVENTION

The invention relates to a marine drive unit with a gyrostabiliser, andespecially to a marine outboard motor assembly incorporating agyrostabiliser.

The marine drive unit of the present invention will preferably be in theform of an outboard motor assembly having a gyrostabiliser and it willbe convenient to describe the invention in this exemplary context. Itwill be understood, however, that the invention is not limited to thatparticular embodiment, but may be embodied in other marine drive units,such as a sterndrive or a pod drive unit.

BACKGROUND OF THE INVENTION

The following discussion of background in this specification should inno way be considered an admission that such background is prior art, northat such background is widely known or forms part of the common generalknowledge in the field in Australia or worldwide.

The structure and operation of marine gyrostabilisers are generallyquite well understood and these devices are gaining increasing adoptionin both commercial and recreational marine vessels. A gyrostabiliserwill typically comprise a spinning flywheel mounted in a gimbal framethat allows two of the three possible rotational degrees of freedom, andthe frame is rigidly mounted within the vessel. The specific way inwhich the flywheel is constrained in rotational motion allows theangular momentum of the spinning flywheel to combine with the flywheel'sprecession oscillation to generate large torques that vary with time todirectly oppose the dynamic rolling motion of the vessel caused bywaves. Without any intervention, the vessel rolling motion combines withthe flywheel angular momentum to cause oscillating precession motion.This then combines with the angular momentum to create a stabilisingtorque, which directly opposes the wave induced rolling motion of thevessel. By arranging the gimbals in a specific way, a roll-stabilisingdevice is created using the naturally occurring physics ofgyro-dynamics, which requires no further intervention to function. Anexample of a marine gyrostabiliser is described in the applicant'sco-pending Australian patent application no. 2017216483 A1, the contentsof which are incorporated herein in their entirety by direct reference.

In use, a gyrostabiliser generates a significant amount of torque whichneeds to be transmitted into the hull of the vessel. Hence, mountingstructures for a gyrostabiliser similar to main engine bearers aretypically designed into the vessel. In addition to the rotatably mountedflywheel, a gyrostabiliser unit may also include a supporting frame forits gimbal bearings, a water pump and a heat exchanger for cooling, avacuum chamber enclosure for the flywheel, and an electrical powersupply. In practice, a gyrostabiliser can be installed in a variety oflocations onboard a vessel, even off centre. As vertical accelerationlevels can reduce the life of the main spin bearings in agyrostabiliser, however, locating a gyrostabiliser unit aft of midshipsis generally preferred.

Due to the relatively complex nature of gyrostabiliser units, and theirassociated cost and incorporation into the structure of a vessel, theyhave tended to find use only on larger recreational and commercialmarine vessels. It would therefore be desirable to provide a newgyrostabiliser arrangement that is both suitable and accessible for usein smaller recreational vessels.

SUMMARY OF THE INVENTION

According to one aspect, the invention provides a marine drive unit,comprising:

a mounting assembly for mounting the drive unit to a hull of a marinevessel, especially to a transom at a stern of a marine vessel, themounting assembly configured for substantially rigid attachment to thehull, and especially to the transom;

a drive casing enclosing at least part of a drive transmission of thedrive unit, at least part of the drive casing being configured to bearranged outboard of the vessel and connected to the hull of the vessel,especially to the transom, via the mounting assembly; and

a gyrostabiliser included in or on the mounting assembly or the drivecasing.

In this way, the invention is able to provide a marine drive unitembodied in the form of an outboard motor, a sterndrive unit, or a poddrive unit in which a gyrostabiliser is integrated for use on smallerboats and other small marine vessels. By integrating the gyrostabiliserinto the drive unit in this manner, it is possible to simplify thegyrostabiliser by eliminating the duplication of systems or componentsotherwise found in both the drive units and the gyrostabiliser units,such as water pumps, electrical supply, housing and supportingstructures, sound attenuation, and safety enclosures. Further, itenables a gyrostabiliser to be installed in the vessel simply bychanging an outboard motor, or a sterndrive or pod drive, and thusrequires little or no modification to an existing boat.

In a preferred embodiment, the mounting assembly has a generally rigidframe for substantially rigid attachment to the hull, especially to thetransom but alternatively to a base of the hull. In this regard, thegyrostabiliser may be integrated or incorporated in the mountingassembly such that a shaft of the flywheel of the gyrostabiliser ismounted for rotation with respect to and supported by the frame of themounting assembly, typically via gimbal bearings. Thus, thesubstantially rigid frame of the marine drive unit mounting assembly,preferably attached outboard of the transom, may also serve as thesupporting structure for the gyrostabiliser for transmitting torque fromthe gyrostabiliser to the hull of the vessel. Furthermore, the transomof the vessel, where outboard motors and sterndrive units are usuallymounted, is an area subjected to lower vertical acceleration, and thusone that is most suitable for gyrostabilisers. More particularly, thesemounting areas and structures for outboards and sterndrives are designedto accommodate the significant forces associated with propelling thevessel and are ideally suited to transmit the gyrostabiliser's torqueinto the hull of the vessel. The substantially rigid frame of themounting assembly configured for attachment to the hull, and especiallyto the transom, preferably includes a housing that encloses thegyrostabiliser. The enclosure provided by the mounting assembly can thusprovide environmental and safety protection for the gyrostabiliser.Thus, a vacuum chamber that typically, but not always, encases the gyroflywheel may not be required.

In another embodiment, the frame of the mounting assembly of the marinedrive unit is configured to be attached or mounted to the hull such thatit is at least partially inboard of the hull; for example, at leastpartially inboard of the transom. According to an embodiment, therefore,the marine drive unit may have the gyrostabiliser arranged forward ofthe transom. In the case of the marine drive unit being an outboardmotor, the mounting assembly may comprise a transom bracket, at leastpart of which is configured to be arranged forward of the transom. Byincorporating the gyrostabiliser with the transom bracket in this way,the gyrostabiliser can be integrated in the outboard motor assembly suchthat it will not rotate with the motor during turning or transmit loadthrough the steering bearing of the outboard motor.

In another preferred embodiment, the substantially rigid frame of themounting assembly may be configured for substantially rigid attachmentto a base of the hull, and preferably through, a base of the hull. Inthis embodiment, therefore, the drive unit may be configured as a poddrive unit. In this embodiment, the gyrostabiliser may be readilyincorporated into a top, side, or rear of an upper gear casing of a poddrive unit. As with the sterndrive embodiment, the structure supportingthe pod drive is both significant and substantially rigid and may besuitable for transmitting to the hull the forces created by thegyrostabiliser with little or no modification.

In a preferred embodiment, therefore, the invention provides a marinedrive unit comprising:

a mounting assembly for mounting the drive unit to a hull of a marinevessel, especially to a base of the hull of the vessel, the mountingassembly configured to be substantially rigidly attached the hull;

a drive casing enclosing at least part of a drive transmission of thedrive unit, at least part of the drive casing being configured to bearranged outboard of the vessel and connected to the hull of the vesselvia the mounting assembly; and

a gyrostabiliser incorporated in or on the mounting assembly and/or thedrive casing.

Because, as noted above, the structure and operation of marinegyrostabilisers are generally quite well-understood, this specificationdoes not aim to provide a detailed description of the basic componentsof a gyrostabiliser, such as the flywheel, flywheel shaft, gimbalbearings, or the like. Rather, this specification directs the skilledreader to other publications for a description or explanation of thosecomponents.

In a preferred embodiment, the drive casing of the marine drive unit ispivotally connected to the mounting assembly for pivoting movementrelative to the vessel hull, and especially to the transom, about atleast one of: a substantially horizontal axis for raising and loweringthe drive casing, and a substantially vertical axis for steering themarine vessel. If the gyrostabiliser is incorporated in the mountingassembly, the drive casing is therefore pivotally movable relative tothe gyrostabiliser in this embodiment.

In an alternative preferred embodiment, at least part of the drivecasing is substantially rigid for mounting and supporting at least partof the drive transmission thereon, and the gyrostabiliser is integratedor incorporated in the drive casing such that the shaft of the flywheelof the gyrostabiliser is rotationally mounted with respect to andsupported by the substantially rigid part of the drive casing, typicallyin laterally arranged gimbal bearings. In this embodiment, therefore,the gyrostabiliser may be integrated or incorporated (i.e. mounted andsupported) in and/or on the drive casing, as opposed to the mountingassembly. In this way, the drive casing outboard of the vessel may serveas the supporting structure for the gyrostabiliser and also fortransmitting torque from the gyrostabiliser to the vessel hull via itsconnection to the mounting assembly, which is designed to be rigidlyattached to the hull, especially to the transom. The drive casingpreferably substantially encloses the gyrostabiliser. The enclosure ofthe drive casing can thus provide environmental and safety protectionfor the gyrostabiliser. As a result, a vacuum chamber that typically,but not always, encases the gyro flywheel may not be required.

As noted above, in the case of an outboard motor or stern drive unit,the drive casing is typically pivotally connected to the mountingassembly for pivoting movement relative to the hull, and especiallyrelative to the transom, about at least one of: a substantiallyhorizontal axis to raise and lower the drive casing, and a substantiallyvertical axis to steer the marine vessel. Thus, in an embodiment withthe gyrostabiliser integrated or incorporated in the drive casing, thegyrostabiliser may be arranged to be pivotally movable with the drivecasing relative to the mounting assembly. Importantly, however, pivotingof the drive casing about the horizontal axis (i.e. to raise or lowerthe drive casing) does not typically occur during travel. Althoughpivoting movement of the gyrostabiliser about a substantially verticalaxis (i.e. during steering) may cause some interference with ordisturbance of the stabilising effect of the flywheel (which may alsorotate about a vertical axis), it is envisaged that any suchinterference or disturbance will be minimal as the degree or extent ofsuch steering movement will usually only be significant when manoeuvringat low speed and in areas that are often quite sheltered, e.g. inharbours or marinas.

In a preferred embodiment, the drive casing may enclose substantially anentire drive transmission of the drive unit and preferably also enclosesan engine or motor that provides power to the drive transmission. Inthis regard, the marine drive unit may be preferably provided in theform of an outboard motor. In such an embodiment, where thegyrostabiliser is integrated or incorporated in the drive casing—e.g.with the shaft of the flywheel of the gyrostabiliser rotationallymounted with respect to and supported by the substantially rigid part ofthe drive casing, typically in lateral gimbal bearings—there are twomain positions contemplated for location of the gyrostabiliser; namely(i) at the forward side or region of the drive casing, desirably abovethe mounting assembly, and (ii) at an aft side or region of the drivecasing, desirably at about the level or height of the mounting assembly.By integrating a gyrostabiliser into an outboard motor according to theinvention, a separate heat exchanger for the gyrostabiliser can beeliminated by utilising the outboard's seawater cooling system. Further,sound damping provisions for the engine can also be used for thegyrostabiliser.

In at least one embodiment, the invention therefore provides a marinedrive unit, e.g. an outboard motor, for a marine vessel, comprising: anengine or power plant, such as an internal combustion engine; a drivetransmission for transmitting or transferring mechanical power generatedby the engine or power plant to a propeller shaft, i.e. for generatingpropulsion for the vessel; a casing that houses or at least partiallyencloses the engine and/or the drive transmission; a mounting assemblyconfigured to mount the outboard motor to a hull, e.g. to a transom, ofthe marine vessel; and a gyrostabiliser arranged in or on the mountingassembly or the casing. It will be noted that the engine or power plantof the marine drive unit may include a two-stroke, a four-stroke ordiesel internal combustion engine, or it may also comprise one or moreelectric motor.

In an embodiment, the mounting assembly of the outboard motor comprisesa substantially rigid mounting bracket configured to be secured to thetransom of the vessel, e.g. via releasable clamping bolts, and thegyrostabiliser is arranged in or on the mounting assembly such that ashaft of a flywheel of the gyrostabiliser is rotationally mounted and/orsupported on the rigid mounting bracket. In this regard, the mountingassembly will typically include a housing that encloses thegyrostabiliser.

In another embodiment, at least part of the casing of the outboard motoris substantially rigid for mounting and supporting the drivetransmission therein and/or thereon, and the gyrostabiliser is arrangedin the casing such that a shaft of a flywheel of the gyrostabiliser isrotationally mounted and/or supported in or on the substantially rigidpart of the casing.

In another preferred embodiment, the marine drive unit is provided inthe form of a sterndrive unit.

In a further preferred embodiment, as already noted, the marine driveunit may be configured as a pod drive unit.

According to another aspect, the invention provides a marine vessel,especially a boat, that comprises or incorporates a marine drive unit ofthe invention according to any one of the embodiments described above.

With a marine drive unit according to the invention, the main supportingframe of the gyrostabiliser can be eliminated by integrating thegyrostabiliser into the structural frame elements of an outboard,sterndrive or pod drive unit, such as the engine cylinder block orheads, the main gear casing, the lower leg casing, or the mountingflanges and brackets. Furthermore, as the invention requires little orno modifications to an existing boat or marine vessel structure, agyrostabiliser can be installed in the vessel simply by exchanging anoutboard motor or sterndrive or pod drive. This creates a retrofitmarket for gyrostabilisers and opens up a new replacement market foroutboard motors, stern-drive units, and pod drive units.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention and advantagesthereof, exemplary embodiments of the invention are explained in moredetail in the following description with reference to the accompanyingdrawing figures, in which like reference signs designate like parts andin which:

FIG. 1 is a schematic side view of a marine outboard motor illustratingthree possible positions A, B, C for a gyrostabiliser integratedaccording to embodiments of the invention;

FIG. 2 is a schematic rear perspective view of a marine outboard motorillustrating the three positions for a gyrostabiliser shown in FIG. 1 ;

FIG. 3 is a schematic front perspective view of a marine outboard motorillustrating the three positions for a gyrostabiliser shown in FIG. 1 ;and

FIG. 4 is a schematic side view of a marine pod drive unit according toan embodiment of the invention.

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrateparticular embodiments of the invention and together with thedescription serve to explain the principles of the invention. Otherembodiments of the invention and many of the attendant advantages willbe readily appreciated as they become better understood with referenceto the following detailed description.

It will be appreciated that common and/or well understood elements thatmay be useful or necessary in a commercially feasible embodiment are notnecessarily depicted in order to facilitate a more abstracted view ofthe embodiments. The elements of the drawings are not necessarilyillustrated to scale relative to each other. It will also be understoodthat certain actions and/or steps in an embodiment of a method may bedescribed or depicted in a particular order of occurrences while thoseskilled in the art will understand that such specificity with respect tosequence is not actually required.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIGS. 1 to 3 of the drawings, a marine drive unit 1according to the invention is embodied as an outboard motor and is shownin three views. Each of these drawing figures illustrates alternativeembodiments of the marine drive unit 1.

The marine drive unit or outboard motor 1 comprises a mounting assembly2 for mounting the outboard motor 1 to a transom (not shown) at thestern of a marine vessel (not shown) and a drive casing 3 that enclosesan engine and a drive transmission of the outboard motor 1. Agyrostabiliser 4 is shown integrated in the outboard motor 1 in threedifferent possible positions A, B, C and each of these positions A, B, Crepresents an alternative embodiment of the marine drive unit oroutboard motor 1.

Firstly, considering integration of the gyrostabiliser 4 in the outboardmotor 1 at position A, it will be appreciated that the gyrostabiliser 4is incorporated in the mounting assembly 2, which is configured forsubstantially rigid attachment to the transom of the vessel. In thisregard, the mounting assembly 2 comprises a substantially rigid frame 5(e.g. comprised of steel) that includes a bracket 6 to be securelyfastened or attached to the transom of the vessel via fasteners, such asbolts, especially releasable threaded clamping bolts, as is known in theart. As seen in FIG. 1 , the gyrostabiliser 4 is mounted and supportedon the rigid frame 5 of the mounting assembly 2 in a position that willbe outboard of the vessel and aft of the bracket 6, arranged between thebracket 6 and the drive casing 3 of the outboard motor 1. In thisregard, the gyrostabiliser 4 is enclosed within a housing 7 on the rigidframe 5 of the mounting assembly 2 such that the shaft S of the flywheelF of the gyrostabiliser 4 is rotationally mounted with respect to andsupported by the frame 5 via laterally arranged gimbal bearings (notshown). The housing 7 integrated with the rigid frame 5 of the mountingassembly 2 provides both environmental protection for the gyrostabiliser4 as well as safety and sound attenuation for users of the marine vesselduring operation the gyrostabiliser 4. The location of the housing 7 onthe frame 5 also enables the gyrostabiliser 4 to utilise the water pumpand electrical supply of the outboard motor 1 during operation.

The drive casing 3 of the outboard motor 1 encloses the engine (notshown) below an upper cowling or cover 8 of the casing 3 in what isreferred to as the power-head of the outboard motor 1, and a gearbox anddrive shaft (not shown) of the drive transmission within a mid-section 9and a lower section or base 9′ of the casing 3 (i.e. below thepowerhead), which then delivers or transmits power to a screw orpropeller P of the outboard motor 1 via a propeller shaft. The drivecasing 3 is pivotally connected to the mounting assembly 2 at a hinge orpivot joint 10 for pivoting movement relative to the transom about asubstantially horizontal axis X for raising and lowering the drivecasing 3. The drive casing 3 is also pivotally connected to the mountingassembly 2 for pivoting movement relative to the transom about asubstantially vertical axis Y for steering the vessel, and this axis issubstantially aligned with the rotational axis Y of the flywheel shaft Sof the gyrostabiliser 4. As such, the drive casing 3 is configured to bepivotally movable about the axes X, Y relative to the gyrostabiliser 4in position A in this embodiment.

Secondly, considering an embodiment in which the gyrostabiliser 4 isintegrated in the drive unit or outboard motor 1 at position B, it willbe seen that the gyrostabiliser 4 in this instance is incorporated inthe drive casing 3, at least part of which drive casing 3 (below anupper cowling or cover 8 that provides engine access) is substantiallyrigid (e.g. formed of steel) for mounting and supporting the engine anddrive transmission therein. In this position B, the gyrostabiliser 4 isthus incorporated (i.e. mounted and supported) within the drive casing 3at a forward side or region of the drive casing 3 above the mountingassembly 2, as opposed to in or on the mounting assembly 2 as shown inposition A. In this way, the drive casing 3 may serve as both a housingfor the gyrostabiliser 4—i.e. to protect the gyrostabiliser 4 againstseawater and environmental influences—and as a supporting structure forthe gyrostabiliser 4—i.e. for transmitting torque from thegyrostabiliser 4 to the vessel hull via its connection to the mountingassembly 2, which, in turn, is substantially rigidly attached to thetransom (not shown).

As noted above, the drive casing 3 is here pivotally connected to themounting assembly 2 for pivoting movement relative to the transom abouteach of a substantially horizontal axis X to raise and lower the drivecasing, and a substantially vertical axis Y to steer the marine vessel.In this embodiment, therefore, the gyrostabiliser 4 is pivotally movablewith the drive casing 3 relative to the mounting assembly 2. However,pivoting of the drive casing 3 about the horizontal axis X to raise orlower the drive casing 3 will not typically occur during travel.Although pivoting movement of the gyrostabiliser 4 about thesubstantially vertical axis Y for steering may cause some interferencewith or disturbance of the stabilising effect of the flywheel F (whichrotates about a substantially vertical axis Y′), it is envisaged thatany such interference or disturbance will be minimal as the degree orextent of steering movement about axis Y will usually only besignificant when manoeuvring at low speed and in areas that aretypically quite sheltered, e.g. in harbours or marinas. By incorporatingthe gyrostabiliser 4 within the drive casing 3, the safety andenvironmental protection, as well as sound attenuation, already providedby this casing 3 for the engine and transmission of the drive unit 1 canthen be employed for the gyrostabiliser 4. Again, the gyrostabiliser 4of this embodiment is also able to take advantage of the water pump andelectrical supply of the outboard motor 1 during operation.

Thirdly, considering integration of the gyrostabiliser 4 in the outboardmotor 1 at position C, it will be seen that the gyrostabiliser 4 in thisinstance is incorporated within the drive casing 3 at an aft side orregion of the drive casing at about the level or height of the mountingassembly 2. In position C, the drive casing 3 again serves as both ahousing and a supporting structure for the gyrostabiliser 4 fortransmitting torque from the gyrostabiliser 4 (which rotates about asubstantially vertical axis Y″) to the hull of the vessel via itsconnection to the mounting assembly 2, which, in turn, is substantiallyrigidly attached to the transom. In this regard, the gyrostabiliser 4may be supported in the casing 3 with the shaft S of the flywheel Frotatably mounted in laterally arranged gimbal bearings (not shown). Theoutboard motor 1 of the invention will preferably be of a higher powerrating, such as 50 Hp and above (e.g. 100-500 Hp), although smalleroutboard motors 1 of a power below 50 Hp are technically feasible, butpotentially less commercially feasible.

With reference now to FIG. 4 of the drawings, a marine drive unit 1 isshown in the form of a pod drive unit. The pod drive unit 1 includes amounting assembly 2 for securely mounting the pod drive unit 1 to a baseof a hull H of a marine vessel in a manner as is known in the art. Thepod drive unit 1 further comprises a drive casing 3 that interconnects aoutput shaft (not shown) from an engine or power plant E of the poddrive unit 1 with a gearbox and drive train or drive transmission withina mid-section 9 and a lower section 9′ of the casing 3, with the lowersection 9′ incorporating a screw or propeller P on a propeller shaftmounted outboard of the hull H. In this embodiment, a gyrostabiliser 4incorporating a flywheel F rotatably mounted on a shaft S for high-speedrotation about the axis Y is integrated on the drive casing 3 of the poddrive 1 enclosed within its own housing 7 such that the shaft S of theflywheel F is rotationally mounted with respect to and supported in thehousing 7 on the casing 3 via gimbal bearings (not shown). Again, therigid structure of the drive casing 3, specifically the mid-section 9,which is securely fastened to the hull H of the vessel serves totransmit the stabilising forces generated by the gyrostabiliser to thehull H. As before, the arrangement in this embodiment can eliminate theduplication of systems or components otherwise found in both the poddrive unit 1 and gyrostabiliser, like water pump, electrical supply,housing, supporting structure, sound attenuation, and safety enclosure.A similar configuration may apply for an embodiment of a stern driveunit according to the invention. Again, power ratings above 50 Hp arepreferred for the pod drive and stern drive units.

Although specific embodiments of the invention are illustrated anddescribed herein, it will be appreciated by persons of ordinary skill inthe art that a variety of alternative and/or equivalent implementationsexist. It should be appreciated that each exemplary embodiment is anexample only and is not intended to limit the scope, applicability orconfiguration of the invention in any way. Rather, the foregoing summaryand detailed description will provide those skilled in the art with aconvenient road map for implementing at least one exemplary embodiment,it being understood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope as set forth in the appended claims and theirlegal equivalents. Generally, this application is intended to cover anyadaptations or variations of the specific embodiments discussed herein.

It will also be appreciated that the terms “comprise”, “comprising”,“include”, “including”, “contain”, “containing”, “have”, “having”, andany variations thereof, as used throughout this document are, unless thecontext requires otherwise, intended to be understood in an inclusive(i.e. non-exclusive) sense, such that the process, method, device,apparatus, or system described herein is not limited to those features,integers, parts, elements, or steps recited but may include otherfeatures, integers, parts, elements, or steps not expressly listedand/or inherent to such process, method, device, apparatus, or system.Furthermore, the terms “a” and “an” used herein are intended to beunderstood as meaning one or more unless explicitly stated otherwise.Moreover, the terms “first”, “second”, “third”, etc. are used merely aslabels, and are not intended to impose numerical requirements on or toestablish a certain ranking of importance of their objects. In addition,reference to positional terms, such as “lower” and “upper”, used in theabove description are to be taken in context of the embodiments depictedin the figures, and are not to be taken as limiting the invention to theliteral interpretation of the term but rather as would be understood bythe skilled addressee in the appropriate context.

1. A marine drive unit, comprising: a mounting assembly for mounting thedrive unit to a hull of a marine vessel, especially to a transom at astern of the marine vessel, the mounting assembly configured forsubstantially rigid attachment to the hull, and especially to thetransom; a drive casing enclosing at least part of a drive transmissionof the drive unit, the drive casing configured to be arranged outboardof the marine vessel and to be connected to the hull, especially thetransom, of the vessel via the mounting assembly; and a gyrostabiliserincorporated in one of the mounting assembly and the drive casing.
 2. Amarine drive unit according to claim 1, wherein the mounting assemblyhas a substantially rigid frame for substantially rigid attachment tothe hull, especially the transom, and wherein the gyrostabiliser isincorporated in the mounting assembly such that a shaft of a flywheel ofthe gyrostabiliser is rotationally mounted with respect to and supportedby the frame of the mounting assembly.
 3. A marine drive unit accordingto claim 2, wherein the substantially rigid frame of the mountingassembly includes a housing that encloses the gyrostabiliser.
 4. Amarine drive unit according to claim 1, wherein the drive casing ispivotally connected to the mounting assembly for pivoting movementrelative to the hull, especially the transom, about at least one of asubstantially horizontal axis for raising and lowering the drive casing,and a substantially vertical axis for steering the marine vessel,wherein the drive casing is pivotally movable relative to thegyrostabiliser.
 5. A marine drive unit according to claim 1, wherein atleast part of the drive casing is substantially rigid for mounting andsupporting said at least part of the drive transmission thereon, andwherein the gyrostabiliser is incorporated in the drive casing such thata shaft of a flywheel of the gyrostabiliser is rotationally mounted withrespect to and supported by the substantially rigid part of the drivecasing.
 6. A marine drive unit according to claim 5, wherein the drivecasing substantially encloses the gyrostabiliser, and wherein arotational axis of the flywheel is in use substantially vertical.
 7. Amarine drive unit according to claim 5, wherein the drive casing ispivotally connected to the mounting assembly for pivoting movementrelative to the hull, especially the transom, about at least one of asubstantially horizontal axis to raise and lower the drive casing, and asubstantially vertical axis to steer the marine vessel, wherein thegyrostabiliser is pivotally movable with the drive casing relative tothe mounting assembly.
 8. A marine drive unit according to claim 1,wherein the drive casing encloses substantially an entire drivetransmission of the drive unit and preferably also an engine or motorproviding power to the drive transmission.
 9. A marine drive unitaccording to claim 8, wherein the marine drive unit is in the form of anoutboard motor.
 10. A marine drive unit according to claim 1, whereinthe marine drive unit is in the form of a sterndrive unit.
 11. A marinedrive unit according to claim 1, wherein the marine drive unit is in theform of a pod drive unit.
 12. An outboard motor for a marine vessel, theoutboard motor comprising: an engine or power plant, preferably aninternal combustion engine; a drive transmission for transmitting ortransferring mechanical power generated by the engine or power plant toa propeller shaft; a casing which houses or at least partially enclosesthe engine and/or the drive transmission; a mounting assembly configuredto mount the outboard motor to a hull, especially to a transom, of themarine vessel; and a gyrostabiliser arranged in or on the mountingassembly or the casing.
 13. An outboard motor according to claim 12,wherein the mounting assembly comprises a substantially rigid mountingbracket configured to be secured to the transom of the vessel, and thegyrostabiliser is arranged in or on the mounting assembly such that ashaft of a flywheel of the gyrostabiliser is rotationally mounted and/orsupported on the rigid mounting bracket.
 14. A marine drive unitaccording to claim 13, wherein the mounting assembly has a housing thatencloses the gyrostabiliser.
 15. A marine drive unit according to claim12, wherein at least part of the casing is substantially rigid formounting and supporting the drive transmission therein, wherein thegyrostabiliser is arranged in the casing such that a shaft of a flywheelof the gyrostabiliser is rotationally mounted and supported in or on thesubstantially rigid part of the casing, and wherein a rotational axis ofthe flywheel is in use substantially vertical.
 16. A marine vessel,especially a boat, comprising a marine drive unit, said marine driveunit comprising: a mounting assembly for mounting the drive unit to ahull of the marine vessel, especially to a transom at a stern of themarine vessel, the mounting assembly configured for substantially rigidattachment to the hull, and especially to the transom; a drive casingenclosing at least part of a drive transmission of the drive unit, thedrive casing configured to be arranged outboard of the marine vessel andto be connected to the hull, especially the transom, of the vessel viathe mounting assembly; and a gyrostabiliser incorporated in one of themounting assembly and the drive casing, wherein the gyrostabiliser inuse operates to oppose a rolling motion of the vessel.
 17. A marinevessel according to claim 16, wherein the mounting assembly has asubstantially rigid frame for substantially rigid attachment to thehull, especially the transom, and wherein the gyrostabiliser isincorporated in the mounting assembly such that a shaft of a flywheel ofthe gyrostabiliser is rotationally mounted with respect to and supportedby the frame of the mounting assembly.
 18. A marine vessel according toclaim 16, wherein the drive casing is pivotally connected to themounting assembly for pivoting movement relative to the hull, especiallythe transom, about at least one of a substantially horizontal axis forraising and lowering the drive casing, and a substantially vertical axisfor steering the marine vessel, wherein the drive casing is pivotallymovable relative to the gyrostabiliser.
 19. A marine vessel according toclaim 16, wherein at least part of the drive casing is substantiallyrigid for mounting and supporting said at least part of the drivetransmission thereon, wherein the gyrostabiliser is incorporated in thedrive casing such that a shaft of a flywheel of the gyrostabiliser isrotationally mounted with respect to and supported by the substantiallyrigid part of the drive casing, and wherein a rotational axis of theflywheel is in use substantially vertical.
 20. A marine vessel accordingto claim 16, wherein the drive casing encloses substantially an entiredrive transmission of the drive unit and preferably also an engine ormotor providing power to the drive transmission.